The present invention concerns a device for punching work pieces in an internal high-pressure forming tool including a punching die that is guided displaceably in a bore, and a drive with which the punching die can be moved back and forth between an in-use position and a non-use position.
A device of this type is known from U.S. Pat. No. 5,398,533. The device described there contains a punching die that is integrated in the internal high-pressure forming tool. The punching die, which can move back and forth in a bore, is supported on the rear side by a wedge-shaped surface of a slide that can be driven manually or automatically and that is displaceable transverse to the movement direction of the punching die. In order to move the punching die in its bore, the slide must be constantly moved back and forth, so that the punching die moves up and down along the wedge surface of the slide. Based on the internal pressure that is applied on the slide via the punching die and that exists in the hollow profile to be punched, the sliding surfaces of the rear side of the punching die and the wedge surface of the slide rubbing against each other wear down relatively quickly during use of the punching die and the slide, Furthermore, the response time of the slide for its displacement path is rather long and impedes the quick completion of the punching process and, therefore, the efficient manufacturing process of the hollow profile to be punched.
In addition, a significant construction space must be provided for the forming tool to be able to place the slide. Often, however, such space is not available, because of the tightly dimensioned accommodation in the tool and/or due to complex processes of the tool form.
As a rule, a hydraulic cylinder is used today for driving a punching die, as is depicted, for example, in German document DE 197 52 171 A1. These very cost-intensive hydraulic cylinders are installed into forming tools, whereby appropriate recesses must be provided, creating large machining operation expenditures. These recesses also lead to a significant weakening of the stability of otherwise solid forming tools. Based on the high tension in a forming tool created by the internal high pressure, such weaknesses can lead to the destruction of the tool. In addition, the use of hydraulic cylinders presupposes corresponding costly control engineering.
One object of the invention is to develop a device as mentioned above in such a way that the punching of work pieces in the internal high-pressure forming tool is enabled in a simple and space-saving manner.
This object is achieved according to the invention by having the drive include a pressure fluid and a pressure transfer device that is elastically expandable via the pressure fluid between a base firmly attached to the tool and a punch head of the punching die, with the pressure transfer device having a partition which at least indirectly abuts the punch head.
By designing the drive for the punching die in the form of a pressure transfer device and a pressure fluid such that the pressure transfer device is elastically expandable according to the invention, the drive can be built having a conceivably small volume. Just an elastic de-location of a partition of the pressure transfer device is necessary for actuating the punching die, with the partition in effective contact with the punch head. The pressure transfer device hardly uses any space in the forming tool, particularly in a non-use position. In addition, the pressure fluid energizing the pressure transfer device can be led via channel-type pipelines that can be designed, as desired and according to constructive tool conditions in the forming tool, so that the pipelines only require very little space. An elastic pressure transfer device can be manufactured with simple methods and placed in the forming tool at the punching die while the pipelines required for the pressure fluid can be incorporated without great expenditure in the forming tool. In order to reduce the device expenditure and in order to make the process more economical, a single pressure fluid can actuate simultaneously several punching dies located in the forming tool via the appropriate pressure transfer devices. In addition, it is possible to punch work pieces at places that are otherwise hard or impossible to reach due to the small dimensions of the device according to the invention. Due to the small space requirements for the device according to the invention, the recesses provided for accommodation of the device can be small so that the forming tool, in total, is only minimally weakened with respect to its solid structure. Thus, the internal high-pressure-induced stress produced during the forming process in the tool can be absorbed without any damage by the forming tool. Furthermore, due to the smaller dimensions in reference to the hydraulic cylinders and slides of the pressure transfer devices, more punching dies can be integrated into the forming tool, as the axial distance of the punching dies only depends on the design of the punching dies. The additional punching options that are gained this way can expand advantageously the variety of work pieces that can be manufactured.
According to certain features of the invention, the punching die is equipped with a compression spring that is supported on the one hand by the bottom of the punch head and on the other hand by the section of a first stepped expansion of the bore. In principle it is conceivable according to the invention that the pressure transfer device is connected with the punch head via its partition in such a way that the punching die is lifted or lowered according to the fluid pressure through expansion or contraction of the pressure transfer device. Here, however, it is not guaranteed that the punching die in a non-use position is always flush with its punching front with the cavity of the forming tool. Undesired impressions and dents can result under certain circumstances on the work piece. In order to assume a defined non-use position that guarantees a flush position of the front of the punching die with the cavity, the compression spring is located at the punching die that sets it back as planned. The punch head is supported then by the pressure transfer device, which assumes a defined position in the forming tool in its non-use position. In order to guarantee the flush position, the prestress of the compression spring must be set appropriately.
According to other features of the invention, the punch head and the pressure transfer device are located within a second stepped expansion of the bore. This layout is designed because of the at least indirect energizing of the pressure transfer design at the punch head. Through a second stepped design, the punching die is given a defined position in the in-use-position, as its bottom can be supported by the section of the expansion step. In order to avoid having the pressure transfer device extrude at the side of the punch head due to the pressure fluid, the diameter of the punch head and the diameter of the expansion must be aligned with each other in such a way that the punch head has play in the expansion that is appropriately reduced.
According to additional features of the invention, the second stepped expansion is intersected by a channel that runs transverse to the expansion and where the pressure transfer device is located. Through the inclusion of the channel, the pressure transfer device can be inserted easily during set-up of the forming tool at the correct destination location and the pressure fluid can be fed without the formation of an additional channel simultaneously via the channel to the pressure transfer device. In addition, the channel running in a transverse direction to the expansion offers support and/or installation surfaces for the pressure transfer device so that it is kept in the prescribed position after its installation. In addition, the pressure transfer device can be exchanged easily via the channel if retooling seems to be required, for example due to signs of wear on the pressure transfer device. Several punching positions can be installed in a space-saving fashion in the forming tool with the appropriate pressure transfer device via this channel, which does not necessarily have to run in a straight line, but can also comprise laterally bent segments and/or height differences. They can be arranged almost anywhere in the forming tool.
According to other features of the invention, the base is formed by a locking plate that is fastened to the forming tool and that covers the channel and/or the expansion towards the exterior. Based on a design that is open at one of the longitudinal sides of the channel, the pressure transfer device(s) can be inserted in a simple fashion into the forming tool. In addition, any desired route of the channel can be incorporated with a high level of precision, for example with milling. The locking plate, which, for example could be screwed to the forming tool, closes the channel at its open longitudinal side. Here the side of the locking plate facing the forming tool forms the base plate for the support of the pressure transfer device. The pressure transfer device can also be attached to this base plate, whereby screws or clamps are conceivable. In any case, the locking plate practically forms a partition of a pressure chamber, in which the pressure fluid is accepted. This means that the pressure fluid can be stressed in the channel and that it remains in the forming tool. In addition, the rigid locking plate prevents expansion of an appropriately formed pressure transfer device to all directions under pressure such that it might explode. Thus, the expansion of the pressure transfer device has a preferred direction, which is the direction of the mobile punching die.
According to additional features of the invention, the pressure transfer device is hollow and contains the pressure fluid, whereby it is connected at least at one end to a controllable high pressure generating system. Using this special pressure transfer device design, the pressure fluid can be guided in a simple and space-saving manner. In addition, the pressure fluid does not wet the forming tool, so that no corrosion occurs on the forming tool. On the other hand, no provisions for sealing the forming tool are necessary, which reduces the design expenditure for the forming tool. Based on the controllability of the high pressure generating system, to which the pressure transfer devices are connected, the pressure of the pressure fluid and, therefore, the degree of the expansion can be fine-tuned to a great extent, which results in further improvement of the process safety during the punching operation.
According to other especially preferred features of the invention, the pressure transfer devices are designed in the form of tubes. In addition to the fact that a pressure transfer device of such a design can be inserted extremely easily in the channel, the tube-shaped design offers the advantage that several punching dies can be controlled with just one pressure transfer device, which drastically reduces the multitude of parts of the device according to the invention. In addition, a tube-shaped pressure transfer device can be easily produced as a segment of a cut-to-length infinite strand with very low costs.
According to other preferred features of the invention, the pressure transfer device is a membrane that is fastened to the base and that is energized with the controlled pressure fluid. In order to guide the pressure fluid, a channel-shaped fluid pipeline is integrated into the forming tool. Due to the surface design of the membrane, an appropriately formed pressure transfer device is even more space-saving than a hollow design of a pressure transfer device.
According to further features, the pressure transfer device directly abuts the punch head with its partition. The number of components according to the invention is further reduced and simplified through the direct energizing of the punch head through the pressure transfer device. This design form is especially space-saving as the intermittent component is foregone.
According to other features, the pressure transfer device is located in a rigid guide rail that abuts the punch head and that is located in the bore with only little tolerance. Due to the location of the pressure transfer device in a rigid guide rail, which only has little tolerance in the bore of the punching die, extrusion of the pressure transfer device, which is under high pressure, at the punch head towards the area of the punch shaft is prevented and no jamming takes place at the punching die that would make it dysfunctional. The energizing process by the pressure transfer device only takes place indirectly due to the layout of the guide rail abutting the punch head.
According to especially preferred features, the supporting area of the guide rail is larger than the punch head surface. Thus, the surface that acts upon the punching die has been enlarged, whereby less pressure must be applied due to the large usable area while keeping the punching power constant. In other words, the same punching power of the punching die can be achieved with lower fluid pressure levels. Due to the lower fluid pressure requirement, the use of smaller-built fluid high pressure generating systems with reduced power is possible without any loss in the process safety of the punching process.
Additional features provide that the guide rail forms the punch head. This in turn enables the direct energizing of the punch head by the pressure transfer device so that another component is omitted, saving space through the integration of the punch head in the guide rail, and so that the advantages of the larger supporting area of the guide rail mentioned are maintained.
According to yet other features of the invention, the punch shaft is attached detachably to the guide rail. If the cutting edge of the punching die is worn, therefore, just the punch shaft or the guide rail can easily be replaced in order to fine tune the amount of punching force exactly with the respective requirements—while the fluid pressure is maintained—via a change in the supporting area of the guide rail.
According to still further features of the invention, the pressure fluid feed line for the drive of the punching die is fluidically coupled with a fluid high pressure generating system for the purpose of generating an internal high pressure to form the work piece. In this way, the supply system of the pressure fluid is significantly simplified by utilizing the fluid high pressure generating system that is used already for forming the work piece and the pressure fluid fed by it via a bypass pipeline.
A process of operating the device is also claimed. The invention is explained in greater detail using examples shown in drawings.